config: just DeciderURL, not Host/Port

addresses review comment ava-labs/awm-relayer#344 (comment)
and ava-labs/awm-relayer#344 (comment)

README.md

@@ -291,11 +291,9 @@ The relayer is configured via a JSON file, the path to which is passed in via th
 
   - The AWS region in which the KMS key is located. Required if `kms-key-id` is provided.
 
-`"decider-host": string`
+`"decider-url": string`
 
-`"decider-port": unsigned integer`
-
-- The network location of a service implementing the gRPC service defined by `proto/decider`, which will be queried for each message to determine whether that message should be relayed. If a port is specified but a host is not, the host is assumed to be `localhost`. If a host is specified then a port is required.
+- The URL of a service implementing the gRPC service defined by `proto/decider`, which will be queried for each message to determine whether that message should be relayed.
 
 ## Architecture
 

config/config.go

@@ -8,8 +8,6 @@ import (
 	"errors"
 	"fmt"
 	"net/url"
-	"strconv"
-	"strings"
 
 	"github.com/ava-labs/avalanchego/ids"
 	"github.com/ava-labs/avalanchego/utils/constants"
@@ -61,8 +59,7 @@ type Config struct {
 	SourceBlockchains      []*SourceBlockchain      `mapstructure:"source-blockchains" json:"source-blockchains"`
 	DestinationBlockchains []*DestinationBlockchain `mapstructure:"destination-blockchains" json:"destination-blockchains"`
 	ProcessMissedBlocks    bool                     `mapstructure:"process-missed-blocks" json:"process-missed-blocks"`
-	DeciderHost            string                   `mapstructure:"decider-host" json:"decider-host"`
-	DeciderPort            *uint16                  `mapstructure:"decider-port" json:"decider-port"`
+	DeciderURL             string                   `mapstructure:"decider-url" json:"decider-url"`
 
 	// convenience field to fetch a blockchain's subnet ID
 	blockchainIDToSubnetID map[ids.ID]ids.ID
@@ -124,18 +121,8 @@ func (c *Config) Validate() error {
 	}
 	c.blockchainIDToSubnetID = blockchainIDToSubnetID
 
-	if c.DeciderPort != nil {
-		portStr := strconv.FormatUint(uint64(*c.DeciderPort), 10)
-
-		host := c.DeciderHost
-		if len(host) == 0 {
-			host = "localhost"
-		}
-
-		uri := strings.Join([]string{host, portStr}, ":")
-
-		_, err := url.ParseRequestURI(uri)
-		if err != nil {
+	if len(c.DeciderURL) != 0 {
+		if _, err := url.ParseRequestURI(c.DeciderURL); err != nil {
 			return fmt.Errorf("Invalid decider URI: %w", err)
 		}
 	}

main/main.go

@@ -10,7 +10,6 @@ import (
 	"net/http"
 	"os"
 	"runtime"
-	"strconv"
 	"strings"
 
 	"github.com/ava-labs/avalanchego/api/metrics"
@@ -178,10 +177,7 @@ func main() {
 
 	relayerHealth := createHealthTrackers(&cfg)
 
-	deciderClient, err := createDeciderClient(
-		cfg.DeciderHost,
-		cfg.DeciderPort,
-	)
+	deciderClient, err := createDeciderClient(cfg.DeciderURL)
 	if err != nil {
 		logger.Fatal(
 			"Failed to instantiate decider client",
@@ -454,23 +450,15 @@ func createApplicationRelayersForSourceChain(
 	return applicationRelayers, minHeight, nil
 }
 
-/* if port is nil, neither a client nor an error will be returned.
- * if is non-nil, a client will be constructed
- * if host is an empty string, a default value of "localhost" is assumed. */
-func createDeciderClient(host string, port *uint16) (*grpc.ClientConn, error) {
-	if port == nil {
+// create a client for the "should send message" decider service.
+// if url is unspecified, returns a nil client pointer
+func createDeciderClient(url string) (*grpc.ClientConn, error) {
+	if len(url) == 0 {
 		return nil, nil
 	}
 
-	if len(host) == 0 {
-		host = "localhost"
-	}
-
 	client, err := grpc.NewClient(
-		strings.Join(
-			[]string{host, strconv.FormatUint(uint64(*port), 10)},
-			":",
-		),
+		url,
 		grpc.WithTransportCredentials(insecure.NewCredentials()),
 	)
 	if err != nil {

tests/utils/utils.go

@@ -191,8 +191,6 @@ func CreateDefaultRelayerConfig(
 		)
 	}
 
-	var deciderPort uint16 = 50051
-
 	return config.Config{
 		LogLevel: logging.Info.LowerString(),
 		PChainAPI: &config.APIConfig{
@@ -208,8 +206,7 @@ func CreateDefaultRelayerConfig(
 		SourceBlockchains:      sources,
 		DestinationBlockchains: destinations,
 		APIPort:                8080,
-		DeciderHost:            "localhost",
-		DeciderPort:            &deciderPort,
+		DeciderURL:             "localhost:50051",
 	}
 }